The advent of low cost, reliable imaging devices, based on a variety of silicon technologies, and in particular CMOS technology, combined with an improved cost/performance ratio for displays capable of meeting automotive specifications, and an increasing application rate of video monitor displays for automotive navigation systems or as part of the driver interface to a wide variety of vehicle systems, has led to an increasing use of cameras or imaging sensors designed to give the driver a view of those areas around the vehicle which are not in the normal direct field of view of the driver, typically referred to as “blind spots”. These areas include the region close to the front of the vehicle, typically obscured by the forward structure of the vehicle, the region along the passenger side of the vehicle, the region along the driver's side of the vehicle rearward of the driver, and the area or region immediately rearward of the vehicle which cannot be seen directly or indirectly through the rear view mirror system. The camera or imaging sensor may capture an image of the rearward (or sideward or other blind spot area) field of view, and the image may be displayed to the driver of the vehicle to assist the driver in backing up or reversing or otherwise driving or maneuvering the vehicle. The use of electronic cameras in these applications significantly increases the driver's knowledge of the space immediately surrounding the vehicle, which may be of importance prior to and during low speed maneuvers, and thus contributes to the safe completion of such maneuvers.
It is thus known to provide a camera or imaging sensor on a vehicle for providing an image of a scene occurring exteriorly or interiorly of the vehicle to a driver of the vehicle. Such a camera may be positioned within a protective housing, which may be closed about the camera or sensor and secured together via fasteners or screws or the like. For example, a metallic protective housing may be provided, such as a die cast housing of aluminum or zinc or the like. In particular, for camera sensors mounted on the exterior of a vehicle, protection against environmental effects, such as rain, snow, road splash and/or the like, and physical protection, such as against road debris, dirt, dust, and/or the like, is important. Thus, for example, in known exterior camera sensor mounts, a butyl seal, such as a hot dispensed butyl seal, or an O-ring or other sealing member or material or the like, has been provided between the parts of the housing to assist in sealing the housing to prevent water or other contaminants from entering the housing and damaging the camera or sensor positioned therein. However, such housings typically do not provide a substantially water tight seal, and water droplets thus may enter the housing. Furthermore, any excessive vibration of the camera sensor, due to its placement (such as at the exterior of the vehicle), may lead to an undesirable instability of the image displayed to the driver of the vehicle. Also, such cameras or sensors are costly to manufacture and to implement on the vehicles.
Such vehicle vision systems often position a camera or imaging sensor at an exterior portion of a vehicle to capture an image of a scene occurring exteriorly of the vehicle. The cameras, particularly the cameras for rearward vision systems, are thus typically placed or mounted in a location that tends to get a high dirt buildup on the camera and/or lens of the camera, with no easy way of cleaning the camera and/or lens. In order to reduce the dirt or moisture buildup on the lenses of such cameras, it has been proposed to use hydrophilic or hydrophobic coatings on the lenses. However, the use of such a hydrophilic or hydrophobic coating on the lens is not typically effective due to the lack of air flow across the lens. It has also been proposed to use heating devices or elements to reduce moisture on the lenses. However, the use of a heated lens in such applications, while reducing condensation and misting on the lens, may promote the forming of a film on the lens due to contamination that may be present in the moisture or water. Also, the appearance of such cameras on the rearward portion of vehicles is often a problem for styling of the vehicle.
Typically, based on consumer preference and at least a perceived improved ability to extract information from the image, it is desired to present a color image to the driver that is representative of the exterior scene as perceived by normal human vision. It is also desirable that such imaging devices or systems be useful in all conditions, and particularly in all lighting conditions. However, it is often difficult to provide a color imaging sensor which is capable of providing a clear image in low light conditions. This is because conventional imaging systems typically have difficulty resolving scene information from background noise in low light conditions.
Silicon-based cameras may be responsive to light in the visible and near infrared portions of the spectrum. It is known to filter out the infrared portion of the energy available to the camera in order to maintain an appropriate color balance. When this is done, the camera sensitivity may be less than if the near infrared and infrared light was received and used by the camera. Depending on the imaging technology used, the minimum sensitivities currently economically available for automotive cameras are typically in the range of 1 to 2 lux and may maintain a reasonable image quality at light levels at or above such levels. However, the conditions on a dark cloudy night where moonlight is obscured, and/or in rural situations in which there is no source of artificial lighting, may result in a scene illumination as low as about 0.01 lux. While the technology continues to improve the low light sensitivity of silicon based cameras, it is not expected that 0.01 lux capability will become available in the foreseeable future. Other technologies may be capable of such sensitivity, but are not sufficiently cost effective for general application in the automotive industry.
Therefore, there is a need in the art for a camera housing that overcomes the shortcomings of the prior art, and a need in the art for an imaging system that may provide clear, satisfactory images during all driving or lighting conditions, and thus overcomes the shortcomings of the prior art imaging systems.